The invention relates to a thrust washer for planet gears of a planetary gearbox. The thrust washers are arranged with their positioning bore hole on the planet gear pins that are fixed in a planet carrier and contact both sides of the planet gears, which are supported rotatably by a rolling bearing on the planet gear pin. For lubricant supply, the planet gear pin is provided with an axial lubricant through hole and a radial lubricant through hole branching off from the axial hole and the thrust washer is provided with axial through holes.
Thrust washers of this type are already known in a wide variety of embodiments. They are used for the axial stop of the planet gear and for protecting the non-hardened planet carrier and also the planet gear from wear. Here, with a flat end surface, the planet gear contacts a similarly flat stopping surface of the thrust washer. The planet gear is provided with a continuous bore hole, with which it is held rotatably on the planet gear pin with the help of a bearing. This bearing can be formed, for example, by a needle collar or also by a cageless needle set. Therefore, according to the type of bearing, either the bearing cage or the ends of the bearing needles contact the thrust washers. The thrust washers are usually stamped from sheet metal. The surface of the thrust washers is either ground or coated. The selection of the material for the washers and their surface quality, as well as their surface hardness, is essentially dependent on the known friction relationships.
However, very often the lubricating relationships at the contact points between the thrust washers and the end surfaces of the planet gears are unsatisfactory. In this case, bronze washers are also used as thrust washers. Now and then, two thrust washers made from different materials, one next to the other, are also used or multiple-layer thrust washers, for example, plated metal plates, are used. Here, the materials steel and bronze are combined with one another. This arrangement takes into account the different stopping and friction relationships between the planet gear and the thrust washer on one hand and the thrust washer and the planet carrier on the other hand.
Also, through a corresponding configuration of the thrust washers, the lubricant circulation within the planetary gearbox and especially at the bearing of the planet gear is influenced in a positive way. The lubricant circulation in the bearing of the planet gear and the lubrication of the stopping surfaces of the thrust washers in the contact area with the planet gear is achieved through oil grooves formed in a targeted way in the surface of the thrust washers or through axial through holes.
Such a thrust washer is previously known, for example, from DE 35 02 076 C1. This thrust washer has two ends formed as flat stopping surfaces and is provided with an angular opening, through which lubricant is to be fed to the bearing. Another thrust bearing is previously known from DE 198 04 734 A1. It is embodied as a flat steel ring, whose ends are provided with impressions and whose positioning bore hole is provided with through holes. Such thrust washers are also previously described in DE 44 18 693 C1. Finally, in DE 40 09 968 A1, a composite thrust washer is presented, which comprises a steel and a copper washer. The inner steel thrust washer exhibits a hardness of 700 to 1500 HV (diamond penetrator hardness number), while the outer copper thrust washer should have a hardness of 200 to 350 HV.
For these thrust washers, it is disadvantageous that for axial contact of the planet gear on the thrust washer, under unfavorable conditions, the lubricant film at the contact points can break down or be interrupted. The result is inadequate lubrication and premature wear at the contact points, which in the extreme case can lead to loss of the entire planetary gearbox. It is further disadvantageous that such thrust washers are relatively complicated and consequently are also expensive to manufacture.